PROJECT SUMMARY/ABSTRACT This K23 application proposes a research and career development plan for Dr. Elizabeth Stenger, a pediatric hematologist/oncologist specializing in blood and marrow transplantation at Emory University, who is a young investigator establishing her career in patient-oriented clinical and translational research. The support of a K23 award would allow Dr. Stenger to develop into an independent investigator with expertise in hematopoietic cell transplantation (HCT) for non-malignant diseases, including sickle cell disease (SCD), and in the use of cellular therapy to decrease the immune-mediated complications of HCT, including graft rejection and graft-versus- host disease. To achieve these long-term goals, Dr. Stenger has formulated the following short-term objectives to be accomplished through this K23 proposal: 1) to acquire the skills needed to conduct phase I/II clinical trials, specifically using cellular therapies; 2) to develop clinical expertise in HCT for SCD, particularly with unrelated and mismatched donors; 3) to acquire training in regulatory aspects of clinical research needed to apply for and maintain an IND; and 4) to gain advanced training and experience in clinical trial methodology and biostatistics. Dr. Stenger has assembled a mentoring team that will be led by Dr. Jacques Galipeau and Dr. Lakshmanan Krishnamurti, who have been successfully co-mentoring Dr. Stenger as a KL2 scholar. As co- primary mentors, their respective expertise in translational research using novel immunotherapeutics (including cell therapy) and in clinical research in HCT for SCD is a significant strength to Dr. Stenger's proposal. The mentoring team will be enhanced by the involvement of Dr. Cynthia Wetmore, who as Director of the Center for Clinical and Translational Research and of Developmental Therapeutics has expertise in conducting phase I/II clinical trials, and by Dr. Gregory Gibson, who as the Director of the Center for Integrative Genetics at the Georgia Institute of Technology has expertise in genomic assays and bioinformatics. SCD affects approximately 100,000 Americans and millions of individuals worldwide, and despite advances in medical treatment such as hydroxyurea and chronic transfusion, individuals with SCD have significant morbidity and early mortality. HCT is the only available curative therapy for SCD, with excellent outcomes following matched related donor transplant. Unfortunately, a cure cannot be offered to most patients as the majority lack a matched related or unrelated donor. Haploidentical family members are an attractive donor option, but graft rejection remains a significant barrier to success. Recipient T lymphocytes play a critical role in graft rejection, highlighting the need for novel T lymphocyte directed therapies. Mesenchymal stromal cells (MSCs) are rare, multipotent cells present in normal bone marrow that are an attractive cell-based immunotherapeutic due to their dual function in hematopoiesis and immunomodulation. Pre-clinical studies have demonstrated that MSCs can promote HSC engraftment, and early clinical trials have established safety and possible efficacy. Although MSCs have been described as immunoprivileged, studies suggest that donor source and cryopreservation impact MSC function, and these may account for differences in efficacy seen between pre-clinical and clinical studies. Dr. Stenger has conducted studies to show that MSCs can be expanded successfully from the bone marrow of individuals with SCD and that they deploy phenotypical and functional properties consistent with guidelines by the International Society for Cellular Therapy. The proposed research plan seeks to perform the first clinical trial using fresh, autologous MSCs to enhance engraftment in patients with severe SCD following haploidentical transplant. Aim 1, within the confines of a phase I clinical trial, will determine the safety and tolerability of infusing escalating doses of autologous MSCs in this setting. Aim 2 will evaluate the potential efficacy of the MSC product through both standard clinical engraftment endpoints in addition to laboratory-based research endpoints, including novel studies using RNASeq. Aim 3 will evaluate the potency of the MSC product, both by in vitro assays of MSC immunomodulation and support of hematopoiesis. Completion of these research aims will establish support for the subsequent phase II clinical trial as well as provide the MSC dosing schedule and laboratory-based efficacy endpoints. The requested 4 years of K23 support for Dr. Stenger's research plan and career development will be critical in establishing her as an independent clinician-scientist. Dr. Stenger's previous clinical and research training in HCT for non-malignant diseases and in pre-clinical cellular therapy studies are a significant strength to this proposal. Dr. Stenger will benefit from the extensive research environment and clinical care infrastructure at Emory University, which has one of the largest SCD programs in the country and where >50 curative transplants have been performed, many through clinical trials. This, in addition to formal training in clinical trials methodology and bioinformatics, will allow Dr. Stenger to reach her long-term goal of leading research efforts to expand the use of curative HCT for non-malignant diseases, including SCD, through the use of novel immunotherapeutics.